Some blind people have dreams of vivid colors. That includes people who have been completely blind their entire lives. Why or how this is possible is being researched. I'll see if I can find the piece about it.

People who have extreme color blindness have also experienced dreams of colors they cannot see.

Here is Helen Keller on the subject:

Once in my dreams I held in my hand a pearl. I have no memory-vision of a real pearl. The one I saw in my dreams must, therefore, have been a creation of my imagination. It was a smooth, exquisitely molded crystal. ... My pearl was dew and fire, the velvety green of moss, the soft whiteness of lilies.

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Some philosophers say the description of color is what is known as qualia -- a subjective quality of conscious experience. Examples of qualia are the way a rose smells, the taste of a rich dessert, the green of freshly watered grass or the red of a sunset. Basically it is almost impossible for a normally sighted person to describe the experience of red to a blind person. You could use an analogy like "red looks hot" or perhaps something even more scientific like "red is the color you see when light of 700 nm wavelength is directed at you" but such descriptions are incapable of providing a complete description of the experience.

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The most vivid picture I ever experienced I heard with my ears As the words flowed from the mouth Of a woman who could not see. With her voice she applied the colors Subtle shading and light. When she was done, I saw the scene in my mind Better than I could have with my eyes

I wrote this about an encounter I had with an artist who had lost her sight but could still picture things - especially color in her mind.